/Engine/Source/Editor/UnrealEd/Classes/Editor/EditorEngine.h
Warns the user of any hidden levels, and prompts them with a Yes/No dialog for whether they wish to continue with the operation. No dialog is presented if all levels are visible. The return value is true if no levels are hidden or the user selects "Yes", or false if the user selects "No".
false if the user selects "No", true otherwise.
bool WarnAboutHiddenLevels ( [UWorld](API\Runtime\Engine\Engine\UWorld) * InWorld, bool bIncludePersistentLvl ) const